a. Field of the Invention
The present invention relates to digital signal manipulation and, more particularly, to performing wipe functions on compressed MPEG video.
b. Description of the Prior Art
A very common video switching effect is a wipe. A wipe is essentially the switching between two or more sources of video incrementally over the course of several frames. There are several ways in which a wipe can be effected. One such way is a horizontal sweep where video from a second source replaces video from a first source with the sweep taking a number of frames for completion. Another, more complicated way to effect a sweep, is by a circular wipe. In the circular wipe, the new or second video source starts out as a small circle within the original or first video source and then progressively replaces the first source with larger circles each frame.
Wipes are one of the functions of a production switcher in a television studio. In a digital studio architecture, such as the NIST ATP High Definition Broadcast Technology project, the production switcher operates on streams of video that are, in their lowest level, in an MPEG-2 format. While these streams may be packed in ATM (Asynchronous Transmission Mode) cells, the cells are composed of MPEG-2 video bitstreams that have, at their lowest level, block-based DCT (Discrete Cosine Transform) coefficients.
A desirable goal of processing these MPEG-2 video bitstreams within a studio environment is the ability to manipulate video without leaving the compressed (MPEG) domain.
It is thus an object of the present invention to provide a method and apparatus for effecting manipulation of a compressed video bitstream.
It is further an object of the present invention to provide a method and appparatus for performing a wipe function on compressed video bitstreams, especially MPEG video bitstreams.
It is still further an object of the present invention to provide a method and apparatus for performing wipes of any complexity on MPEG video bitstreams, especially those composed of all I frames.